OS X 10.5.2 introduced a bug that affects several applications that use floating windows (tool palettes, inspectors, etc.,) and pop-out sheet dialogs, including InqScribe and older versions of RealBasic.

Basically, sheet dialogs won't function if you have a floating window open. Close the floating window(s), and the sheet dialog works again. It would appear that the floating window(s) steal the mouse clicks from the sheet dialog. Here's hoping it's fixed in 10.5.3...